Colonoscopy | Cancer Research UK
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A colonoscopy is a test that looks at the inside of your large bowel. You usually have this test in the endoscopy unit of the hospital. The test itself takes about 30 minutes, but you should plan on being at the hospital for up to 4 hours.

Before a colonoscopy

You need to have an empty bowel for the test. So you have to take bowel preparation (laxatives) the day before your appointment. You also have to follow a special diet for 1 or 2 days beforehand. The hospital will give you strict instructions on what you have to do. It is important you follow these carefully.

Having a colonoscopy

The nurse will offer you medicine to make you drowsy (sedation) and painkillers if you want them.

You lie on your left side with your knees bent. A nurse or doctor (colonoscopist) puts a flexible tube called a colonoscope into your back passage and gently passes it up into your bowel. They put a small amount of gas into your bowel so that it is easier to see all of the bowel lining.

The colonoscopist can take photographs of the bowel lining and samples of tissue (biopsies). Any growths in the bowel (polyps) can be removed with a wire loop put down the colonoscope.

If you’ve had sedation, you will go to the recovery area to rest for a couple of hours. You shouldn't drive or drink alcohol for about 24 hours after having the sedative. You will need someone to take you home and stay with you overnight. If you’ve not had any sedation, you can usually go home soon after the test.

You may feel bloated and have some mild cramping pain for an hour or two afterwards.

Possible risks with colonoscopy

Colonoscopy is a safe test for most people. But it does have possible risks. The risks include breathlessness due to a reaction to the sedation, bleeding from the back passage, or a hole in the bowel wall (perforation). These are very rare.

Results

Before you go home, the colonoscopist will tell you if they took any biopsies or removed polyps. You should receive the results in about 2 weeks.

 

What is a colonoscopy?

A colonoscopy looks at the whole of the inside of the large bowel. A doctor or nurse (colonoscopist) uses a flexible tube called a colonoscope. The tube has a small light and camera at one end. The colonoscopist puts the tube into your back passage and passes it along the bowel. They can see the pictures of the inside of your bowel on a TV monitor.

You usually have this test in the endoscopy unit of the hospital. The test itself takes about 30 minutes, but you should plan to be at the hospital for up to 4 hours. The animation shows what to expect when you have a colonoscopy.

View a transcript of the video about having a colonoscopy (opens in a new window).

 

Why you might have a colonoscopy

There are a number of reasons why you may need a colonoscopy. These include

  • To help find the cause of bowel symptoms
  • To look for early signs of bowel cancer as part of the national bowel cancer screening programme, or if you are at high risk of developing bowel cancer
  • As part of your follow up after treatment for bowel cancer
 

Before a colonoscopy

You need to have an empty bowel for the test. This is so the colonoscopist can clearly see the lining of your bowel.

The hospital will give you bowel preparation medicines (laxatives). You take them the day before your appointment. You will have instructions on how and when to take the laxatives. You need to follow these carefully.

You will need to follow a special diet, such as a low fibre diet, for a couple of days before your test. You can't have solid food for 1 or 2 days beforehand. When you start taking the laxatives, it is important to drink plenty of clear fluids. This includes

  • Water
  • Tea or coffee without milk
  • Fizzy drinks or squash (but no drinks with red or purple colouring)

You may be able to have clear soup. The hospital will tell you what you can have.

After taking the laxatives you need to go to the toilet often. The need to go may be very sudden. You may also have stomach cramps. You need to stay at home for at least a few hours after taking the laxatives so that you are close to a toilet.

If you take iron tablets, you usually need to stop taking them a week before your colonoscopy. If you normally take medicines that can cause constipation, such as loperamide (Imodium) or codeine phosphate, you may need to stop taking them about 4 to 7 days beforehand. Your appointment letter will give you details about this.

Contact the endoscopy unit for advice as soon as possible before your appointment if you take medicines to thin your blood such as aspirin, clopidogrel or warfarin, or you are diabetic.

 

At the hospital

When you arrive at the endoscopy unit, a nurse will talk to you about what to expect. They will answer any questions you may have. They will ask you about your medical history, and take your blood pressure, pulse and oxygen levels. This is to make sure you are fit and well enough to have the test.

The nurse will ask whether you want to have a medicine to make you drowsy (sedation). You can also have painkillers if you want them because a colonoscopy can be uncomfortable. If you have a sedative you may need to stay in the hospital a couple of hours longer than if you don’t have it.

The nurse or a technician will give you a gown to change into. They may also give you paper shorts to wear, which have an opening at the back.

 

Having a colonoscopy

If you have a sedative or painkillers you normally have them as injections into a vein in the back of your hand or arm.  Some hospitals may use gas and air (Entonox) for pain relief instead of sedation. Entonox is a quick acting form of pain relief that you breathe in through a mouth piece.

If you have sedation, you will have oxygen through a tube that fits into your nose (nasal cannulae). The nurse will monitor your oxygen levels.

The colonoscopist will ask you to lie on your left side with your knees bent. They put the colonoscope into your back passage and gently pass it up into your bowel. The tube bends easily so it can pass around the curves in the bowel. The colonoscopist puts a small amount of gas into your bowel so it is easier to see all of the bowel lining.

They can take photographs of the bowel lining and samples of tissue (biopsies). If they see any growths in the bowel (called polyps) they can remove them with a wire loop that they put down the colonoscope. Your doctor may also spray a dye onto the lining of the bowel to make abnormal areas show up more clearly. This is called chromoscopy.

Diagram showing a colonoscopy

You should not feel pain during the test. But it can be uncomfortable when they first put the tube into your back passage and when the tube goes around bends in your bowel.

 

After a colonoscopy

If you’ve had sedation, you go to a recovery area after the test to rest and wait for the sedation to wear off. This can take a couple of hours. The nurse will check your pulse and blood pressure, and offer you something to eat and drink when you are ready.

You shouldn't drive or drink alcohol for 24 hours after having the sedative. So you need someone to take you home from the hospital. If you live alone, they should ideally stay overnight to make sure that you are alright.

If you’ve not had sedation, you can usually go home soon after the test.

You may feel bloated and have mild cramping pain for a few hours afterwards. This is due to the gas that the colonoscopist put into your bowel. It may take up to a week for your bowel habit to go back to normal.

 

Possible risks with colonoscopy

Colonoscopy is a safe test for most people. But like all medical tests it does have possible risks. Doctors make sure the benefits of having the test outweigh these risks.

There is a risk that you may react to the sedation drug, causing difficulty in breathing. Your nurse will monitor your oxygen levels and breathing during and after the test.

After having a biopsy or polyp removed, you may have some bleeding. This is usually a small amount and stops on its own. Rarely, you may need a blood transfusion or surgery to stop the bleeding.

There is a very small risk of making a hole in the bowel wall, called a perforation. Although this is rare, it is serious. You will be admitted to hospital and may have to go to the operating theatre for emergency surgery to repair your bowel wall. You will need strong antibiotics to prevent infection.

Your nurse will give you clear instructions on what to look out for and who to contact if you have any problems at home.

 

The results

Before you go home, the doctor will talk to you about the test and if they had to take any biopsies or remove polyps. If so, you may need to wait up to 2 weeks to get the results. The hospital will send them to your specialist, who will give them to you. If your GP sent you for the test, the results will be sent directly to the GP surgery.

Understandably, waiting for results can make you anxious. Try to remember to ask your doctor how long you should expect to wait for the results. If it is not an emergency, and you haven't heard anything after a couple of weeks, you could phone your doctor’s secretary or GP surgery to check if the results are back.

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Updated: 19 February 2016